PHOSPHOTYROSYL-PROTEIN PHOSPHATASES.
Item
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Title
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PHOSPHOTYROSYL-PROTEIN PHOSPHATASES.
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Identifier
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AAI8423055
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identifier
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8423055
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Creator
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CHERNOFF, JONATHAN.
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Contributor
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Heng-Chun Li
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Date
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1984
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, General
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Abstract
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The phosphorylation of proteins at tyrosine has been implicated in the establishment and maintenance of neoplastic transformation by certain retroviruses, as well as in the regulation of normal cell growth by various polypeptide hormones. Although overall phosphorylation levels are determined by a balance of protein kinase and phosphatase activities, much more attention has been given to the study of tyrosyl-protein kinases than to the corresponding phosphotyrosyl-protein phosphatases. Therefore, a survey was undertaken to determine what enzymatic species possess phosphotyrosyl-protein phosphatase activity. Purified enzymes, including human prostatic acid phosphatase (an enzyme which has traditionally been assayed using the phosphotryosine analog p-nitrophenyl phosphate) and bovine heart phosphoprotein phosphatases-1-4, were examined for phosphotyrosyl-protein phosphatase activity. In addition, extracts of bovine heart and other mammalian tissues were examined for detection of specific phosphotyrosyl-protein phosphatases. Two such enzymes were purified and characterized.;The results of this study indicate that: (a) acid phosphatases selectively dephosphorylate phosphotyrosyl-proteins; (b) phosphoprotein phosphatases-2, -3, and -4, but not -1, display activity toward phosphotyrosyl-proteins, but this activity is much less than that toward phosphoseryl- or phosphothreonyl-proteins; (c) mammalian tissues contain several phosphatase isozymes which are relatively specific for phosphotryosyl-proteins. These include three species separable by anion-exchange chromatography, termed phosphotyrosyl-protein phosphatase Y-1, -2, and -3. When measured at neutral pH in the presence of EDTA, these species represent 33, 55, and 12%, respectively, of the total phosphotyrosyl-protein phosphatase activity in bovine heart extract. Phosphatase Y-1 (M(,r) 13,000), does not bind to DEAE-cellulose at pH 7.0, has an acidic pH optimum, and is associated with acid phosphatase activity. Phosphatase Y-2 (M(,r) 65,000) elutes from DEAE-cellulose at 0.1-0.2 M KCl, has a neutral pH optimum, is stimulated by chelating agents, and has little activity toward p-nitrophenyl phosphate.;In conclusion, (a) all enzymes active toward p-nitrophenyl phosphate appear also to be active toward phosphotyrosyl-proteins; (b) the classical phosphoprotein phosphatases-1-4 have relatively little phosphotyrosyl-protein phosphatase activity; and (c) extracts of mammalian tissues contain multiple species of specific phosphotyrosyl-protein phosphatases.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Biomedical Sciences
